1. Field of the Invention
This invention relates to the field of sense amplifiers, particularly those used to sense input-output lines from a static random access memory cell.
2. Related Application
This application is related to copending application Ser. No. 065,930, filed June 24, 1987, and entitled "Folded-Cascode Configured Differential Current Steering Column Decoder Circuit".
3. Prior Art
In a typical semiconductor memory, contents of the memory are coupled to various devices for input and output of information to and from the memory. Various semiconductor memory architectures incorporate the use of sense amplifiers to read information stored in the memory cells. Initially, data is written into and stored in a memory cell. When this data is to be read from each of these memory cells, a pair of bit lines couple the memory cell to its appropriate sense amplifier. The sense amplifier reads the state of the bit lines and provides the result as an amplified signal on a distribution bus.
In a typical memory array architecture, a plurality of memory cells are arranged in a row and column matrix and normally the columns are coupled to a sense amplifier through a decoder circuit. A word line selects memory cells of a given row of an array and the decoder circuit selects a desired column to the sense amplifier.
Various sense amplifiers are available to perform this function in the prior art. However, prior art sensing schemes achieve sensing by one or more stages of common source differential amplifiers coupled to the input-output (I/O) lines. Typically, these prior art sense amplifiers require the use of level shifters and active loads which are sensitive to process variations.
A common gate MOS differential sense amplifier, which is an improvement over the prior art, is disclosed in U.S. Pat. No. 4,658,160 in which the inventor of that patent is also the current inventor of this application.
The U.S. Pat. No. 4,658,160 discloses a sense amplifier, which is an advantage over the prior art method of providing amplification for sense amplifiers. However, the U.S. Pat. No. 4,658,160 utilizes devices biased in the linear region of transistor operation and is, therefore, dependent on the voltage changes present on the data lines. It is an object of the present invention to provide an improved sense amplifier which is less sensitive to input voltage and current variations and is substantially independent of voltage changes on the data lines.